What two molecules are known to inhibit MAC formation?

The correct answer highlights the roles of CD 59 and S protein in inhibiting the formation of the Membrane Attack Complex (MAC), which is crucial for preventing unwanted cell lysis.

CD 59 is a glycoprotein that binds to the C5b-8 complex, preventing the recruitment and polymerization of C9, which is the last component in MAC formation. By doing so, CD 59 provides a protective mechanism to host cells, ensuring that they are not attacked by the complement system, which could lead to cell damage and inflammation.

S protein, also known as vitronectin, similarly plays a protective role by binding to the C5b-7 complex, inhibiting its ability to insert into cell membranes and initiate MAC formation. This action helps to limit the potential for complement-mediated lysis of host cells and tissues.

Understanding the function of these molecules is critical in immunology and pathology, particularly in the context of autoimmune diseases and complement-related disorders, where MAC formation may have damaging effects on tissues.

In contrast to the correct answer, the other options include molecules that do not directly inhibit MAC formation. For example, while CD 4 and CD 8 are important co-receptors in T cell activation, they do not